Louid speaker



J y 1957 H. w. SULLIVAN 2,797,766

LOUD SPEAKER,

EiledOct. 20, 1953 A Jb 7 1N VEN TOR.

HERBERT W- SULLIVAN 3A: 7 f m/ M ATTORNEY United LOUD SPEAKER Herbert W. Sullivan, New York, N. Y., assignor to David Bogen & Company, Inc., a corporation at New York Application October 20, 1953, Serial No. 387,188

' 9 Claims. (Cl. 181-31) response characteristic of an acoustic diaphragm by causing at least one side of said diaphragm to vibrate in a medium other than air, adapted by its characteristic impedance or capacitance to extend the lower frequency end as compared to that prevailing in air.

Another object of the invention is to cause at least one side of an acoustic diaphragm to vibrate in a gaseous medium which is heavier than air.

'Another object of the invention is to vibrate at least one side of a diaphragm in a gas or gas mixture reducing the velocity of sound waves as compared to that prevailing in air.

. Still further an object of the invention is to increase the characteristic impedance of the diaphragm as compared to that prevailing in air.

Still another object of the invention is to increase the acoustic capacitance of the diaphragm as compared to that prevailing in air.

In a more specific object of the invention, an air tight enclosure containing the acoustic diaphragm is provided with a membrane substantially permeable to the mechanical vibrations of the diaphragm but substantially impermeable to the gaseous medium on either side of the mem braue.

As a further specific object of this invention the diaphragm itself is used as a membrane substantially perme- .able to acoustical vibrations and substantially impermeable to the gaseous medium on either side thereof.

Another specific object of the invention is a horn loud speaker of reduced axial length or increased flare rate provided with a driving mechanism which is gas-tightly closed and attached to a horn which is also gas-tightly closed and provided with a membrane substantially permeable to the acoustical vibrations of the driving mechhorn loud speaker as compared to that of a standard type loud speaker of substantially the same dimensions.

tates Pate t ice Fig. 3 shows another embodiment of the invention involving a Helmholtz resonator.

Figs; 4, 5, 6, 7 and 8 represent further modifications of the invention.

In Fig. 1, the driving mechanism of a horn loud speaker schematically indicated at 1 is contained in a cylindrical enclosure 2. Driving mechanism 1 consists of driving magnet 3 which can be permanent or energized, driving coil 4 and diaphragm'S attached to coil 4. Diaphragm 5 is so mounted in otherwise well known manner as to vibrate in the rhythm of the electrical vibrations impressed upon driving coil 4.

In the driving mechanism shown, the resulting acoustical vibrations are transferred by a pump type of operation into a space 6 formed by exponential horn 7 which is attached to housing 2 of the driving mechanism 1.

In accordance with the invention the front end or opening of space 6 is closed gas-tightly with a membrane 8 of polystyrene, polyethylene or the like plastic which permits passage ofv the vibrations produced by diaphragm 5 to the outside but which does not permit the gaseous medium on either side of the diaphragm to pass from one side to the other. The inside of horn 7 and box 2 is filled with a relatively heavy gas such as SP6 or sulphahexafluoride. Carbon dioxide has also been found to have an eifect increasing or extending the low frequency response.

In experiments underlying this invention it has also been found that a gas or gas mixture reducing the velocity of the sound waves (in SP6 to a value of one third of that in air) or a gas or gas mixture increasing the characteristic acoustic impedance (in SP6 to a value of 70 ohms as compared to a value of 45 ohms prevailing in air) will reduce the lower frequency range from 250 cycles per second to cycles per second as apparent from Fig. 2 wherein the corresponding frequency characteristics in air and SP6 are shown at 9 and 9' respectively.

Other gases or gas mixtures which can be used in accordance with this invention are those increasing the acoustical capacitance as compared to that prevailing in air, such acoustical capacitance beingin turn dependent substantially upon the product of the acoustic density of the gas and its characteristic acoustic impedance with respect to the diaphragm.

In this way-it has become possible for example in the case of a horn loud speaker such as shown in Fig. 1, filled with SP6 to reduce horn length to about one third or increase the flare rate by about three times and yet obtain substantially the same frequency response characteristic as that of a horn of its previous size'and flare rate, but

With a diaphragm operating with both sides against air in the usual manner.

Fig. 3 shows the invention as applied to a diaphragm of conical shape such as indicated at 10 and suspended in an enclosure forming a so-called Helmholtz resonator schematically indicated at 11 which also may be called an R-J enclosure. Such R-J enclosure is of substantially quadrangular shape and is provided at its front with an opening 12 facing diaphragm 10 and gas-tightly closed with a membrane 13 of polystyrene which is attached to the front panel 14 of enclosure 11 in a gas tight or sealed In a further modification as shown in Fig. 4 a conicaldiaphragm 17 is shown suspended in a driving mechanism schematically indicated at 18 and feeding the acoustic vibrations into a relatively short horn 19.

As in previous realizations of the invention the large opening of horn 19 is provided with a membrane which is acoustically permeable but gaseously impermeable and the entire mechanism is supported in a gas-tight enclosure schematically indicated at 20. Gas tightness is achieved with a plastic sealing coat applied to the inner 'wall of enclosure 20.

Enclosure 20 is also provided with a valve schematically indicated at 21 which permits replacement of the gas and also if necessary an evacuation preceding such replacement.

In the modification of the invention shown in Fig. 5 a gas-tight enclosure 22 .is provided with two openings 23, 24. Oneopening, 23, faces the'diaphragm schematically indicated at 25 and the second opening 24 serves as a resonating port in otherwise. well known 'manner. Openings 23, 24 are provided with membranes 26, 27 which in accordance with this invention are acoustically permeable but. gaseously impermeable.

The corresponding improvement in the response characteristic caused by resonating port 24 in combination with the gas filling of enclosure 22 with an appropriate gas in accordance with the invention, increases the low frequency response in about the same manner shown in Fig. 6; the improvement causedby the resonating port is shown by dotted line 28 and the improvement caused by the addition of the gas is shown by dotted line 28.

Fig. 7 shows the invention in a rather simple form of realization in which a conical diaphragm 29 is supported around opening 30 of a gas-tight enclosure 31 and in such a way that diaphragm 29 due to its gas-tight structure and attachment also serves as a membrane separating the frequency reducing gas medium arranged in enclosure 31, from the outside atmosphere.

While in this realization of the invention the extension of low frequency response is less marked than in the case where both sides of the acoustical diaphragm are exposed to a sound velocity reducing, or impedance or capacitance increasing gas, the resulting improvement in low frequency response combined with the simplicity of the structure involved was found suflicient to justify certain practical applications.

Similarly useful effects are obtained in accordance with Fig. 1 when thespace of box 2 is separated by a diaphragm which by its structure and suspension assures gastight division of the space behind diaphragm 5 from the space in front of diaphragm 5. In this case a very heavy gas such as SP6 of rather high pressure for example, several atmospherescan be arranged only in the space of box 2 behind diaphragm 5 i. e. schematically indicated at 32 was found to give sufiicient an increase in acoustical impedance to permit a noticeable reduction of horn length to justify its economical use.

In the modification of Fig. 8 an air-tight loud speaker enclosure 33 is shown to form the lower section or, a compartment of a larger enclosure which is shown in Fig. 8 schematically at 34 in the form of a radio phonograph combination. Compartment 33 of cabinet 34 is gastightly sealed for example by an inner coating35 against the upper section 36 and also against the outer atmosphere.

In compartment 33, membrane 37 covers an opening 38 behind which a loud speaker 39 is arranged in otherwise well known manner.

Here, too, a valve can be provided as schematically indicated at 40 to permit replacement or refilling of the gas after a long time of operation or in the case of repair, and also a preceding evacuation if necessary.

While the invention has not been shown as applied to a microphone, it can easily be used in connection with such a microphone or a loud speaking telephone because the principles underlying this invention apply with more or less the same effect to the conversion of mechanical vibrations into electrical vibrations.

The invention is not limited to the diaphragm, membrane, sealing and gas-structures shown and described.

It can be applied to all types of gases or gas mixtures of appropriate pressures whereby the sound velocity is reduced or acoustic impedance or capacitance are increased to increase low frequency responsive, all this without exceeding the scope of the invention.

I claim:

1. In an apparatus for interconverting acoustical and electrical vibrations, a source of electrical vibrations, a diaphragm resonant at the low frequency end of the response characteristic coupled to said source and supported to vibrate in the rhythm of said electrical vibrations, and a substantially tight enclosure supporting said diaphragm and adapted to transmit the vibrations of said diaphragm from its inside to its outside, said enclosure being filled with a gas other than air having a lower sound velocity than air to permit reduction in size of said enclosure for a predetermined response characteristic as compared to the size of an enclosure filled with air.

2. Apparatus according to claim 1 wherein said enclosure has substantiallythe form of an exponential horn of a size reduced as compared to the size of a horn filled with air with the diaphragm being arranged at the small end of said horn, the large end ofsaid horn being provided with a membrane substantially permeable to the acoustic vibrations of said diaphragm but substantially impermeable to the passage of gaseous medium from one side of said membrane to the other side.

3. Apparatus according to claim '1 wherein said enclosure is in the form of a Helmholtz resonator of a size reduced as compared to the size of a resonator filled with air having an opening and a conical diaphragm arranged behind such opening, said opening being closed by a membrane substantially permeable to the acoustic vibrations of said diaphragm but substantially impermeable to the passage of gaseous medium from one side of said membrane to the other. 7

4. Apparatus according to claim 1 comprising an exponential horn of a size reduced as compared to the size of a horn filled with air cooperating with said diaphragm, both being arranged in said enclosure; said enclosure having an opening substantially coinciding with the opening of said horn and provided with a membrane substantially permeable to the passage of the acoustic vibrations passing from said diaphragm through said horn to said opening, and substantially impermeable to the passage of gaseous medium from one side of said membrane to the other.

5. Apparatus according to claim 1 wherein said enclosure has walls coated at their inside with 'a sealing layer to prevent passage of gaseous medium through said impedance of said diaphragm.

9. Apparatus according to claim 1 wherein said enclosure has an opening, said diaphragm being extended over said opening and forming a portion of said enclosure which is substantially permeableto acoustic vibration but substantially impermeable to the passageof gaseous medium from one side of said-diaphragm tothe other side.

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